There is known a spectrometer for granulometric analysis of particles contained in gases. The spectrometer comprises a chamber through which there is directed a flow of a particle-containing gas, such as air (aerosol), and a light source which emits a beam of light to traverse the aerosol flow. To maintain the laminarity of the aerosol flow at the point of its intersection with the light beam, the aerosol flow is confined in a flow of filtered air.
There is known an optical sensor for determining the quantity of particles in a sample of a fluid. The sensor comprises a flow-through cell with two windows. Passed through the cell is a liquid envelope into which a fluid sample is introduced. The liquid envelope separates the sample from particles on the cell walls and directs, with great accuracy, particles of the sample to the focus of the light beam arriving through the windows provided in the cell.
There is further known a device for granulometric analysis of particles contained in fluids.
The device comprises a feeding channel for the supply of fluid to be analyzed. The feeding channel communicates through a tubular nozzle with a receiving channel which is of a great diameter and arranged coaxially with the feeding channel. Spaced in the annular gap between the tubular nozzle and the walls of the receiving channel are pipes for the supply of pure liquid to form a liquid envelope encompassing the flow of the fluid being investigated. The receiving channel is provided with transparent windows to admit a light flux into the fluid flowing through the channel. The light flux is emitted by a lighting means whose optical axis extends at an angle to the axis of the nozzle.
The device under review further includes a light-sensitive means to receive light reflected from particles contained in the fluid being investigated. The light-sensitive means is arranged so that its optical axis passes through the point of intersection of the axis of the nozzle and the optical axis of the lighting means.
The optical properties of the liquid envelope must be identical with those of the fluid under investigation. Such an identity can best be achieved when the fluid being analyzed and the liquid envelope are of the same composition, but the fluid used to form the liquid envelope is pure, i.e. rid from all foreign particles with sizes in excess of the sensitivity threshold of the light-sensitive means.
The above requirement makes it imperative that the device should include such components as a fluid tank, a pump and a high-performance fluid purifying unit.
In addition, provision must be made for a special means to equalize the velocities of the fluid being investigated and the liquid envelope in order to prevent their mixing at the point where the flow of liquid being investigated is traversed by the light beam, i.e. prevent a transfer of particles from the fluid being analyzed to the liquid envelope.
There is another important consideration: a device of the foregoing type is normally used to analyze different fluids, which necessitates a change of the liquid envelope, keeping in mind that the optical properties of the latter must be identical with those of the fluid subjected to analysis. However, such changes effect the overall rate of analysis and increase the costs involved.